1. Field of the Invention
The present invention relates to an optical pickup apparatus capable of optically recording, reproducing, and deleting information on an information recording medium such as an optical disk.
2. Description of the Related Art
FIG. 11 is a view showing a configuration of an optical pickup apparatus 9 according to a first related art. FIG. 12 is a view showing a light beam-irradiated area 39 on a light detector 98 of the optical pickup apparatus 9. FIGS. 13A and 13B are graphs each showing a relation between displacement and beam quantity balance of the light detector 98.
The optical pickup apparatus 9 includes a laser element 91 for generating a light beam; a polarization beam splitter 92 composed of two right angle prisms that are bonded to each other on total reflection surfaces, either of which surfaces is coated with a polarizing film; a quarter-wave plate 93 formed of an optically anisotropic body, through which two mutually orthogonal polarization components of the light beam being transmitted become different in phase by a quarter of a wavelength of the light beam; a lens 94 through which the light beam transmitted by the quarter-wave plate 93 is converted into a light beam of collimated light; an objective lens 95 through which the light beam emitted by the lens 94 converges; a cylindrical lens 97 which causes astigmatism; and the light detector 98 for converting received light beam into an electric signal. As a recording medium 96, a disc-shaped recording medium is used which optically records and reproduces information.
The light detector 98 has a light receiving portion for receiving light which is partitioned into four divided regions A to D, by an X-axis-wise parting line 81 and a Y-axis-wise parting line 82 in X-Y coordinates. Light is received by the respective divided regions of the light receiving portion, and photoelectric output signals SA to SD are outputted for the respective divided regions in accordance with intensity of the light. A position of the light detector 98 is adjusted so that the outputted photoelectric output signals SA to SD for the respective divided regions of the light receiving portion are equal to each other when the light beams equal in intensity are emitted to the respective divided regions of the light receiving portion in the light beam-irradiated area 39 on the light detector 98. In such a position as above, the light detector 98 is fixed with adhesive, for example, to a housing for supporting the light detector 98.
As a second related art, a focal error detecting device has been disclosed which uses not the astigmatic method but the knife-edge method. In the focal error detecting device, a light detector is partitioned by three parallel parting lines and thus composed of four light receiving elements, and provided with a light blocking means for blocking first-order diffracted light contained in a light beam which has been reflected by a recording medium and is entering the light receiving elements. Owing to the light blocking portion for blocking the first-order diffracted light contained in the light beam which has been reflected by the recording medium and is entering the light receiving elements, a focal error can be detected without influences of the first-order diffracted light beam which is used for detection of tracking errors (refer to Japanese Unexamined Patent Publication JP-A 2-126429 (1990), for example).
As a third related art, an optical head has been disclosed. In the optical head, a light receiving means receives a plurality of light beams split by a first parting line and at least one light blocking region located symmetrically on either side of the first parting line. The first parting line is parallel to a direction optically corresponding to an information track. The light blocking region preferably blocks a part of reflected light beams of overlapped zero-order diffracted light and first-order diffracted light diffracted by the information track. A part of the light beams exhibiting a light intensity distribution highly influenced by inclination of an optical disk is thus removed by the light-blocking region, and a plurality of the reflected light beams are split when received. As a result, it is possible to reduce the offset of tracking error signals attributable to the inclination of the optical disk (refer to Japanese Unexamined Patent Publication JP-A 11-513835 (1999), for example).
In the first related art, a change in ambient temperature, physical impact, or the like matter may cause a positional shift of the light detector 98 fixed to the housing, etc. The positional shift of the light detector 98 induces a change in the light intensity balance. The graph of FIG. 13A shows a change of the light intensity balance relative to X-axis-wise displacement, represented by the expression {(SA+SD)−(SB+SC)}/(SA+SB+SC+SD). The graph of FIG. 13B shows a change of the light intensity balance relative to Y-axis-wise displacement, represented by the expression {(SA+SB)−(SC+SD)}/(SA+SB+SC+SD).
That is to say, the light intensity balance is substantially proportional to the displacement of the light detector 98 and therefore, the positional shift of the light detector 98 increases or decreases the light beam-irradiated area on the light receiving portion of each region, thus causing a problem that the photoelectric output signals SA to SD undesirably change and thus no longer have those adjusted values which are equal to each other. The change of the photoelectric output signals SA to SD leads to breakdown of such a relation that photoelectric output signals SA to SD are equal to each other, resulting in a failure to fall within a desired error range to be detected and thus causing a decrease in controllability.
Also in the second and third related arts, the relation between the change in the light intensity balance and the displacement, of the light detector or light receiving means, is similar to that shown in the graph of FIG. 13B. That is to say, there arises a problem that the shift of the light detector or light receiving means causes the change in output of the light detector or light receiving means, resulting in a failure to achieve the desired error detection.